1. Field of the Invention
The present invention relates to a charged-particle beam writing method and a charged-particle beam writing apparatus. More specifically, the present invention relates to the calculation and correction of a position displacement amount of a charged-particle beam due to a charging effect of a sample.
2. Background Art
With the introduction of a double patterning technique, there has been a demand for enhancement of position accuracy of a photomask. With its demand, there has been a demand for an improvement in pattern placement accuracy in the photomask. It has, however, been known that when a pattern of the photomask is written by an electron beam writing apparatus, a beam irradiation position is displaced or shifted due to a resist charging effect.
As one method for correcting this beam irradiation position displacement, there has been known a method for forming a charge dissipation layer (CDL) on a resist layer and preventing the charging of a resist surface. Since, however, the charge dissipation layer basically has an acid characteristic, it is incompatible with a chemical amplification resist. There is also a need to provide a new facility in order to form the charge dissipation layer, thus causing a further increase in the manufacturing cost of a photomask. Therefore, it is desirable to perform charging effect correction (CEC) without using the charge dissipation layer.
A writing apparatus for calculating a correction amount of a beam irradiation position, based on electric field strength and applying a beam based on the correction amount has been proposed in Japanese Patent Application Laid-Open No. 2007-324175. According to the writing apparatus, a position displacement amount distribution is calculated from an irradiation amount or exposure distribution through a linear response function assuming that a linear proportional relationship is established between the exposure distribution and a charge amount distribution.
According to further discussions of the present inventors, however, it has been found out that the position displacement amount distribution cannot be calculated with satisfactory accuracy assuming that the linear proportional relationship is established between the exposure distribution and the position displacement amount distribution. Therefore, the need for establishing a new model to determine the position displacement amount distribution with high accuracy without using such a linear proportional relationship has arisen.